Step 1Heat oil in a large saucepan over a medium heat. Sauté leek and celery for 5 minutes. Add the garlic; cook, stirring, for 1 minute. Add miso paste and 5 cups of water; whisk to combine and bring to the boil.
Step 2Add the chicken, reduce the heat to low and gently simmer for 10 minutes. Using tongs, transfer chicken to a plate and set aside to cool slightly. Shred the chicken using two forks.
Step 3Meanwhile, cook noodles in a large saucepan of boiling water, following the packet instructions ,or until al dente. Rinse and drain.
Step 4Return chicken to soup with the peas and sugar snap peas. Simmer for 2–3 minutes. Add the bok choy, and simmer until wilted and heated through.
Step 5Divide noodles between four serving bowls. Ladle over hot soup and garnish with shallots.